The objective of this proposed research is a study of the action of histamine on the heart and the receptors which are responsible for its action. This will be done by (a) the use of isolated spontaneously beating atrial tissue to test the effect of histamine, histamine analogues, antihistamines and related drugs on chronotropic activity, (b) the use of electrically driven papillary muscle and atrial strips to study the inotropic effects of histamine (and other drugs) unmodified by changes in rate, (c) the use of enzyme inhibitors which affect both the formation and catabolism of histamine as well as agents which deplete histamine stores, and (d) most important by an attempt to isolate the cardiac histamine receptor by affinity chromatography.